With the development of the broadband network and the trend of the digital technology, the wireless products with wireless transceiving functions are increasingly popular, such as a wireless network access point (AP), a mobile phone, a personal digital assistant (PDA), and a notebook computer. The wireless products not only provide extensive range of functions but also deliver more convenient and effective services. However, the wireless communication products are sensitive to the surrounding electromagnetic waves caused by other wireless communication systems or external noises.
For example, when a wireless product performs the data wireless transmission under a high power state, the high frequency harmonic waves are extremely easily generated by non-linear characteristics of active components, so as to result in an electro-magnetic interference (EMI) emission, which is often the prime contributor to the performance degradation. In order to solve the problem, legal regulations are made in many countries to regulate and restrict illegal input applications and usages of the wireless products. As a result, when the designers and manufactures of the wireless product design a control line of the wireless product, the requirements of the related regulations must be fulfilled and incorporated into the wireless design. Furthermore, the circuit of the wireless product is also affected by the signals of the external electromagnetic wave, such as, radio frequency (RF) wireless signals, to result performance inconsistencies.
Therefore, it is a critical factor for the designers and developers to know how to effectively eliminate the interference and the noise in order to improve the performance of the wireless products. Several conventional methods are proposed to reduce the impact of EMI and RF emissions on wireless communication products, such as the methods disclosed in, ROC Patent No. 521561, U.S. Pat. No. 6,689,670, and U.S. Pat. No. 6,528,866.
Conventionally, an isolation cover is disposed on a circuit board to eliminate emissions related to EMI or RF interference. As shown in FIG. 1, an isolation cover 22 is fully soldered onto a main body 20 of a circuit board 2 by adopting a surface mount technology (SMT), so that the isolation cover 22 can cover part of components on the circuit board 2, such as, the chip(s) located on a surface of the main body 20 of the circuit board 2. A reflow-soldering process is performed on the circuit board 2 through a tin oven (not shown).
However, this conventional method is used a soldering technique called a single-piece fully soldering process to solder the isolation cover 22 entirely onto the main body 20 of the circuit board 2. After the reflow-soldering process, if some of the components underneath the isolation cover 22 fail, a desoldering process must be performed to detach the isolation cover 22 in order to replace the corresponding components. In this manner, the maintenance is costly and time consuming, and the surface of the circuit board main body 20 is easily damaged or deformed, more significantly, the detached isolation cover 22 cannot be reused. As a result, the fabrication cost of the conventional method is extremely high.
Meanwhile, when the isolation cover 22 is disposed onto the circuit board main body 20, the components underneath are entirely covered. The heat generated during the soldering process cannot be effectively dissipated, resulting a temperature differentiation between the components, which leads to a tombstone effect. Thus, the components located in the isolation cover 22 can fail easily.
In order to solve the disadvantage of the single-piece fully soldering technology, a two-pieces fully soldering technology is provided as shown in FIG. 2. A lower frame 24 and an upper cover 26 are used to replace the single piece isolation cover. During assembling process, the lower frame 24 is firstly soldered to the main body 20 of a circuit board 2′, and the upper cover 26 is used to cover the main body 20 of the circuit board 2′ after the circuit board 2′ passing through the tin oven, so that the upper cover 26 can be integrated to the lower frame 24.
However, the requirements of performing the two-pieces fully soldering process are more complicated, and the cost is relatively higher. Furthermore, the lower frame 24 is required to be firstly soldered, and after the circuit board 2′ passing through the tin oven, a second processing is performed on the upper cover 26 for the second time. Thus, the assembling process of this method is more costly.
Both the single-piece fully soldering technology and the two-pieces fully soldering technology require the solder to perform the soldering process, and the heat dissipation is the major problem during the soldering process that can severely damage to the components on the circuit board and the circuit board itself.
From the above-mentioned techniques, the conventional methods have serious drawbacks. Therefore, it is an objective of the present invention to provide a true solution to resolve all the drawbacks, and an improved circuit board of a wireless communication product and a fabrication method that can successfully eliminate the interferences.